I'm with Mike Sullivan. I would much prefer a prequel than a sequel. There would be so much they could cover showing the young Corleones and their climb to the top of the crime world.
I'm also with Deathkiss as far as Andy Garcia too. Don't know if he'd be the best choice, but I think Nicholas Cage would be better for the role. I definitely will see any GFIV with or without AG, but he certainly is not my choice. I'd rather see Leo as a young Sonny than AG as the next Don.

But let's face it, all indications are that AG will be in it. So we'll hope for the best.
TIS